Quantum Networking (Part 4)

Welcome back.

Now that we’ve seen a little about how Q-SYS devices are configured,

let’s take a step back and think about the different types of network traffic.

Specifically thinking about multicast traffic.

Before Multicast, there's Unicast,

where a device is sending a packet point -to -point to another device on the network.

There’s only one destination.

There's also Broadcast – that’s when a device is sending a packet that it wants all devices in that subnet to ‘hear’.

This would have a whole subnet’s worth of receiving devices.

But, what if we only want certain devices on a network to ‘hear’ a given packet?

I have more than one intended receiver,

but I don’t want to broadcast the packet everywhere on the subnet.

That’s where ‘Multicast’ networking comes in.

This technology makes use of a virtualized IP address and MAC address range

to facilitate a dynamic flow of packets to a number of destinations.

The address range is specifically defined from 224.0.0.0 to 239.255.255.255.

The destination MAC address of a multicast stream is calculated with a special OUI,

01-00-5e so that switches and routers know to handle this as a special case.

Switches and routers with the right functionality can be configured

to make sure multicast traffic reaches only the ports that want it.

This functionality is referred to as the Internet Group Management Protocol (or IGMP).

If a given switch doesn’t support IGMP or it isn’t enabled,

then multicast traffic is effectively handled as a broadcast.

Multicast models are typically used for device discovery (such as Q-SYS device discovery)

and multi-destination media streaming that requires a lot of bandwidth.

If these media streams were broadcast, they would bog down the entire network.

Making them multicast streams helps manage the bandwidth used

and makes sure they only go to the right places.

The IGMP protocol allows devices to register for the multicast transmissions that they would like to receive.

The mechanics of this process rely on a few different aspects of the protocol.

IGMP snooping is the feature you’re enabling on the switch to provide this functionality.

This allows for the registration of groups with the switch.

An IGMP querier is then required to maintain the list

of which endpoints would like to receive which multicast streams.

Note there can only be one querier per network.

It asks each device on a regular basis what multicast groups it wants to be a part of.

The multicast routing function actually decides which stream should go to each port

based on the switch’s table of registrations.

That’s ultimately how the bandwidth is limited to only the necessary ports.

There are three versions of the IGMP protocol:

In version 1, groups can be joined, but a device can’t unregister for them.

In version 2, devices can join and leave groups.

And version 3 allows a device to register for groups only transmitted by a specific source.

Note that Q-SYS devices support IGMP V2.

Q-SYS uses a number of multicast elements to do its job.

As I mentioned before, the Q-SYS discovery protocol relies on multicast.

Instances of the Designer software and Q-SYS Cores

send multicast discovery packets in search of other Q-SYS devices.

When this discovery message is ‘heard’ by a Q-SYS device, it sends a unicast reply back to the sender.

Ever notice that you can see a device in Q-SYS configurator that’s on the wrong IP subnet in red?

This is an important observation about multicast traffic.

Since it makes use of virtualized IPs and MACs, it bends the rules a little.

Q-SYS cameras use the Web Discovery protocol for some specialized features.

The precision time protocol is also a multicast technology.

And then finally we have a number of multicast audio and video stream types…AES67 audio is one example.

AES67 streams are ALWAYS multicast.

Note that all multicast media streams must have a distinct address, or we find ourselves in trouble.

It’s kind of like duplicating an IP address on the network.

Of the multicast protocols listed,

only the multicast media streams consume much bandwidth on the network.

One question we get a lot is ‘when do I need to configure IGMP snooping?’

as it can be difficult to configure them on some infrastructures.

Q-LAN streams are unicast, so a standalone Q-SYS audio system,

even a very large one often doesn’t need any IGMP features enabled.

Here are some guidelines that will help you decide if IGMP snooping and filtering is required on your network:

Are there any 100Mbps devices on the network such as TSC7s or Audinate Ultimo devices?

These devices can tolerate much less broadcast traffic than a 1Gbps device.

Do you have multicast video on the network? IGMP is a MUST in this case.

Do you have more than 5 multicast audio streams on the network?

Remember that AES67 makes use of multicast streams for everything.

If your answers to those questions are all ‘no’

then you should be fine to leave IGMP snooping disabled on your switches.

Alright let’s take a break there, and feel free to proceed to the final video whenever you’re ready.